The invention concerns security and/or value documents, for example banknotes, cheques, share certificates, credit cards, software certificates or identity cards or passes, which comprise a support of a paper material with one or more window-shaped openings and a preferably strip-form or thread-form film element.
There is a need for security and/or value documents to be provided with security features which make it difficult to forge those documents and as far as possible to prevent that. It is already known in that respect for security and/or value documents to be provided with transmissive security elements which can be checked when viewed in a transillumination mode and which afford a particularly high level of security against imitation by means of a colour copier.
It has already been proposed in that respect for security threads to be introduced into value documents, which are exposed in region-wise manner at the surface in order to be able to check additional security elements on the thread, for example print patterns, diffraction structures and so forth. Thus for example EP-A-0229645 describes the production of a security paper with an incorporated security element in the form of a thread in which two separate layers of paper are formed, which have regions of smaller thickness or openings. The two paper layers are brought together and the band which serves as a security element is introduced during the operation of bringing them together. In that situation the arrangement can also be so selected that the openings in the two paper layers are in mutually superposed coincident relationship so that the security element is exposed at the same location on the paper web on both sides. That also permits the security element to be viewed in the transillumination mode.
That approach however suffers from the disadvantage that, as security threads must be incorporated into the paper web they may only be of comparatively narrow width in order not to interfere with the paper in itself being held together. That is the case in particular if the paper web is exposed in coincident relationship on both sides in order to permit a security element to be viewed in a transillumination mode. In addition it is necessary here to use security threads of relatively large thickness so that the security threads afford adequate tensile strength in spite of their small width. That thickening effect which occurs in a relatively narrow region results in poor planar positioning of the sheets and thus gives rise to problems in further processing of the value document.
In addition DE-A-4334847 describes a value document in which window-shaped openings are subsequently produced in the support of the value document by means of a stamping or cutting operation. Those openings are then closed by means of a cover film which is transparent at least in region-wise manner and which projects beyond the openings on alt sides and which is fixed on the surface of the support over the full area thereof. That arrangement makes it possible to use a cover film which has one or more security elements and which is of comparatively large dimensions so that, in comparison with the above-described windows which are produced in production of the paper, it is possible to implement larger windows and the thickness of the film element can be reduced. In terms of practical implementation of that procedure however it has been found that here too with relatively large window widths, problems can occur in further processing of the security and/or value documents.